Plasmon-controlled, ultra-bright, excitation-polarization-independent photoluminescence from individual Ag nanoplates

Fluorescent metallic nanoparticles with high quantum yield are highly desirable for optical imaging in the fields of biology and materials science. We investigate the photoluminescence (PL) properties of Ag nanoplates, particularly triangular ones, systematically at the single-particle level under different excitation conditions. We find that their emission is controlled by surface plasmon resonances (SPRs). Because of their high geometric symmetry, the shape and intensity of the PL spectrum from Ag triangular nanoplates are independent of the excitation polarization. Under excitation wavelengths of 473, 532 and 633 nm, the PL quantum yield (QY) of Ag triangular nanoplates is found to be twice that of Au nanorods at similar SPR wavelengths. It can be attributed to the stronger and broader SPR response, which can make the PL more intense not only in the spatial domain but also over a larger range in the frequency domain. Our investigations will extend the application of Ag nanoplates in imaging, labeling, and emitting, especially at the single-molecule level, due to their ultra-bright, stable, and polarization-independent PL. This method to enhance the PL signal, in both the spatial and frequency domains, can be easily expanded to other systems.